Ring Slings---Have two rings that are typical to this style of carrier.  The rings vary in weight, size and color.  These slings come in "one size fits all" usually.  They can accomodate most sizes as needed with the help of the adjustable rings mentioned.  The shoulder can come in different styles and may cup and fold differently depending on style.  Sizing is truly preferential to length the tail comes off the front of the carrier.  Some like a longer tail in front and others care for a shorter version.  Some parents however, do not care for the rings to adjust or tail worn in front.  Rings can often dig inrto shoulders if not worn properly.  Baby can be worn in lots of positions in a ring sling.